Controllable preparation of metal oxide nanoparticles and Ni/CeO2 catalysts by microdroplets extraction and separation technology in mini-channel

The microreactor coupled mini-channel microdroplets extraction and separation technology (MES) was developed by adding polyvinyl alcohol (PVA) into microdroplets, realizing the controllable synthesis of a series of mono-component and multi-component metal oxide nano particles (MONPs). A double-layer surfactant structure composed of Span20 (oil phase surfactant) and PVA (water phase surfactant) was designed as a barrier to intercept and collect the precipitated salt at the microdroplet interface, the addition of PVA reduces the loss of salt components during the extraction process from 41.7 wt% to 1.1 wt%. The size control of mono-component MONPs (CuO, Co3O4, and NiO) was achieved using MES method. Furthermore, in the application direction of preparing multi-component MONPs, the advantages of MES in preparing multi-component catalysts (Ni/CeO2) were verified. TEM, XRD, H2-TPR, CO2-TPD, XPS, BET et al. characterizations have shown that Ni entered the lattice of CeO2 during precipitation to form a Ni-O-Ce solid solution and was therefore highly dispersed in CeO2. Ni/CeO2-MES showed high CO2 conversion and CO selectivity in reverse water gas shift (RWGS) testing compared to Ni/CeO2 catalysts prepared by impregnation method which has excellent thermal stability and can maintain over 99 % CO selectivity even after 50 h of reaction at 600 °C. The MES method was proved to be an efficient synthesis technology for MONPs and can be extended to a variety of metal oxides catalysts.